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《Astronomy& Geophysics》2000,41(4):4.14-4.17
An RAS Meeting was held on 22 June in London to discuss joining the European Southern Observatory and the future of the UK ground-based astronomy programme. Eric Priest reports. 相似文献
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Michał Malinowski 《Acta Geophysica》2013,61(6):1437-1456
Controlled-source seismology (CSS) is the primary source of information regarding the fine structure of the lithosphere. The aim of this paper is to provide an overview of the methods that are commonly used to derive Earth models from CSS data with the focus on the wide-angle reflection/refraction method. Some outlook on the future of the CSS is presented with the special emphasis on the full-wavefield based methods like full-waveform inversion, which brings high level of objectivity into modeling, as well as significantly increases spatial resolution. It is stressed that the researchers should be aware of the limitations of how the elastic parameters transcribe into the actual rock properties which should stimulate them to go beyond the simple P-wave modeling and to build multiparameter Earth models based either on the seismic data or constrained by additional geophysical fields in order to derive sound geological interpretation of their models. 相似文献
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Polglaze J 《Marine pollution bulletin》2003,46(1):33-38
Considerable quantities of food waste can be generated at a rapid rate in ships, particularly those with large numbers of people onboard. By virtue of the amounts involved and its nature, food waste is potentially the most difficult to manage component of a ship's garbage stream, however, in most sea areas it may be dealt with by the simple expedient of direct discharge to sea. As a consequence, only minimal attention is paid to food waste management by many ship and port operators and advisory bodies, and there is a paucity of information in the available literature. The determination that management of ships' food waste is inconsequential is, however, incorrect in many circumstances. Disposal to sea is not always possible due to restrictions imposed by MARPOL 73/78 and other marine pollution control instruments. Effective management of food waste can be critical for ships that operate in areas where disposal is restricted or totally prohibited. 相似文献
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《Journal of Atmospheric and Solar》2000,62(16):1499-1507
It may be possible to calculate the rate of reconnection in the corona by measuring the rate at which the temporary coronal hole formed by a coronal mass ejection (CME) disappears. This calculation is possible if the disappearance of the hole is caused by the same reconnection process which creates the giant X-ray arches associated with CMEs. These arches form just below the vertical current sheet that is created as the CME drags magnetic field lines out into interplanetary space, and they are similar in form to ‘post’-flare loops, except that they often have an upward motion that is different. Instead of continually slowing with time as ‘post’-flare loops do, they move upwards at a rate which increases, or remains nearly constant, with time. This difference has raised doubts about the relevance of reconnection to the formation and propagation of the arches. Using a two-dimensional flux rope model to calculate the size and location of the current sheet as a function of time, we find that the difference between the motion of ‘post’-flare loops and giant arches can be explained simply by the variation of the coronal Alfvén speed with height. 相似文献
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The value of a formally defined Anthropocene for geomorphologists is discussed. Human impacts have been diachronistic, multifaceted and episodic, as demonstrated by the record of alluvial deposition in the UK. Rather than boxing time into discrete eras or periods, modern research uses calendar dates and multiple dating techniques to explore co‐trajectories for a range of human impacts. Despite the value of ‘The Anthropocene’ as an informal concept and as a prompt to useful debate, arriving at a single, generally acceptable formal definition is impractical, and has some disadvantages. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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《Limnologica》2020
Natural ponds are perceived as spatially and temporally highly variable ecosystems. This perception is in contrast to the often-applied sampling design with high spatial but low temporal replication. Based on a data set covering a period of six years and 20 permanently to periodically inundated ponds, we investigated whether this widely applied sampling design is sufficient to identify differences between single ponds or single years with regard to water quality and macrophyte community composition as measures of ecosystem integrity.In our study, the factor “pond”, which describes differences between individual ponds, explained 56 % and 63 %, respectively, of the variance in water quality and macrophyte composition. In contrast, the factor “year” that refers to changes between individual years, contributed less to understand the observed variability in water quality and macrophyte composition (10 % and 7 % respectively, of the variance explained). The low explanation of variance for “year” and the low year-to-year correlation for the single water quality parameter or macrophyte coverage values, respectively, indicated high but non-consistent temporal variability affecting individual pond patterns.In general, the results largely supported the ability of the widely applied sampling strategy with about one sampling date per year to capture differences in water quality and macrophyte community composition between ponds. Hence, future research can be rest upon sampling designs that give more weight to the number of ponds than the number of years in dependence on the research question and the available resources. Nonetheless, pond research would miss a substantial amount of information (7 to 10 % of the variance explained), when the sampling would generally be restricted to one year. Moreover, we expect that the importance of multiple-year sampling will likely increase in periods and regions of higher hydrological variability compared to the average hydrological conditions encountered in the studied period. 相似文献
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New concepts in ecological risk assessment: where do we go from here? 总被引：10，自引：0，他引：10
Through the use of safety factors, the use of single-species test data has been adequate for use in protective hazard assessments and criteria setting but, because hazard quotients do not consider the presence of multiple species each with a particular sensitivity or the interactions that can occur between these species in a functioning community, they are ill-suited to environmental risk assessment. Significant functional redundancy occurs in most ecosystems but this is poorly considered in single-species tests conducted under laboratory conditions. A significant advance in effects assessment was the use of the microcosm as a unit within which to test interacting populations of organisms. The microcosm has allowed the measurement of the environmental effect measures such as the NOAEC(community) under laboratory or field conditions and the application of this and other similarly derived measures to ecological risk assessment (ERA). More recently, distributions of single-species laboratory test data have been used for criteria setting and, combined with distributions of exposure concentrations, for risk assessment. Distributions of species sensitivity values have been used in an a priori way for setting environmental quality criteria such as the final acute value (FAV) derived for water quality criteria. Similar distributional approaches have been combined with modeled or measured concentrations to produce estimates of the joint probability of a single species being affected or that a proportion of organisms in a community will be impacted in a posteriori risk assessments. These techniques have not been widely applied for risk assessment of dredged materials, however, with appropriate consideration of bioavailability and spatial and nature of the data these techniques can be applied to soils and sediments. 相似文献
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We have evaluated all parameters for the calculation of cosmogenic 36Cl production rates and thus surface exposure ages in dolomite and limestone. We found that we can use either of both published negative muon stopping rates until more information is available. The largest uncertainty of the age estimation in the upper meter of rock comes from the 36Cl production rate from Ca spallation and, in the case of 50–100 ppm Cl content, from the production rate of epithermal neutrons, which we estimate at 760 ± 150 neutrons/g_air/yr (1σ). For a sample with representative amounts of Ca and Cl (20 wt% Ca and 50 ppm Cl, or 40 wt% Ca and 100 ppm Cl), the age can be calculated with a precision of 7–10% in the top 1.5 m of the depth profile. Further improvement of 36Cl calculations depends on new calibration of 36Cl production from Ca spallation, re-evaluation of 36Cl production by low-energy neutron capture on 35Cl, as well as of the muon flux and muon capture based on the most recent measurement data. 相似文献
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K. Kauristie T. I. Pulkkinen R. J. Pellinen H. J. Opgenoorth 《Annales Geophysicae》1997,14(11):1177-1185
The AE indices are generally used for monitoring the level of magnetic activity in the auroral oval region. In some cases, however, the oval is either so expanded or contracted that the latitudinal coverage of the AE magnetometer chain is not adequate. Then, a longitudinal chain in the key region would give more information of the real situation, but, of course, only during some limited UT-period. In order to find out the UT coverage of a single meridional chain, we have compared the global AL and AU indices with corresponding local indices determined using data from the meridional part of the EISCAT Magnetometer Cross during the years 1985–1987. A statistical study shows that the local indices are close (within relative error of 0.2) to the global AU and AL during periods 1500–2000 UT ( 1730–2230 MLT) and 2130–0130 UT (000–0400 MLT), respectively. In the middle of these optimal MLT-sectors the EISCAT Cross sees more than 70% of the cases when the global AE chain records activity. Then, also the correlation between the local and global indices is generally good (>0.7). Thus we conclude that five to six evenly located meridional chains are needed for covering all the UT-periods. On the other hand, already the combination of IMAGE, CANOPUS, and the Greenland chains catches 50% of the substorms. Case-studies show that usually during 2130 – 1100 UT the AL achieved from these chains reproduces the real AL with good timing, although it does not follow all transient variations. 相似文献
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Cetacean mass stranding events associated with naval mid-frequency sonar use have raised considerable conservation concerns. These strandings have mostly involved beaked whales, with common pathologies, including "bubble lesions" similar to decompression sickness symptoms and acoustic traumas. However, other cetacean species have also stranded coincident with naval exercises. Possible mechanisms for the strandings include a behavioral response that causes deep divers to alter their diving behavior, which then results in decompression sickness-like impacts. Current mitigation measures during military exercises are focused on preventing auditory damage (hearing loss), but there are significant flaws with this approach. Behavioral responses, which occur at lower sound levels than those that cause hearing loss, may be more critical. Thus, mitigation measures should be revised. A growing number of international bodies recognize this issue and have urged increasing scrutiny of sound-producing activities, but many national jurisdictions have resisted calls for increased protection. 相似文献
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What can we learn from the projections of changes of flow patterns? Results from Polish case studies 总被引：1，自引：1，他引：0
Mikołaj Piniewski Hadush Kidane Meresa Renata Romanowicz Marzena Osuch Mateusz Szcześniak Ignacy Kardel Tomasz Okruszko Abdelkader Mezghani Zbigniew W. Kundzewicz 《Acta Geophysica》2017,65(4):809-827
River flow projections for two future time horizons and RCP 8.5 scenario, generated by two projects (CHASE-PL and CHIHE) in the Polish-Norwegian Research Programme, were compared. The projects employed different hydrological models over different spatial domains. The semi-distributed, process-based, SWAT model was used in the CHASE-PL project for the entire Vistula and Odra basins area, whilst the lumped, conceptual, HBV model was used in the CHIHE project for eight Polish catchments, for which the comparison study was made. Climate projections in both studies originated from the common EURO-CORDEX dataset, but they were different, e.g. due to different bias correction approaches. Increases in mean annual and seasonal flows were projected in both studies, yet the magnitudes of changes were largely different, in particular for the lowland catchments in the far future. The HBV-based increases were significantly higher in the latter case than the SWAT-based increases in all seasons except winter. Uncertainty in projections is high and creates a problem for practitioners. 相似文献
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Jin Li Andrew D. HeapAnna Potter Zhi HuangJames J. Daniell 《Continental Shelf Research》2011,31(13):1365-1376
Spatially continuous data of environmental variables is often required for marine conservation and management. However, information for environmental variables is usually collected by point sampling, particularly for the marine region. Thus, methods generating such spatially continuous data by using point samples to estimate values for unknown locations become essential tools. Such methods are, however, often data- or even variable-specific and it is difficult to select an appropriate method for any given dataset. In this study, 14 methods (37 sub-methods) are compared using samples of mud content with five levels of sample density across the southwest Australian margin. Bathymetry, distance-to-coast, slope and geomorphic province were used as secondary variables. Ten-fold cross validation with relative mean absolute error (RMAE) and visual examination were used to assess the performance of these methods. A total of 1850 prediction datasets are produced and used to assess the performance of the methods and the effects of other factors considered. Considering both the accuracy and the visual examination, we found that a combined method (i.e., random forest and ordinary kriging: RKrf) is the most robust method. This method is novel, with a RMAE up to 17% less than that of the control. No threshold in sample density was detected in relation to prediction accuracy. No consistent patterns are observed between the performance of the methods and data variation. The RMAE of three most accurate methods is about 30% lower than that of the best methods in previous publications, highlighting the robustness of the methods selected in this study. The implications and limitations of this study are discussed and a number of suggestions are provided for further studies. 相似文献